The road to Tozeur crosses this vast salt lake, where chemicals in the water affect its colour so that in bright sunlight some stretches can be red, some green and others deep blue. In the afternoon, if conditions are right, mirages often occur too.
Mirages occur when there are layers of air of various temperatures and densities next to each other. The light rays are bent on the way to the eye so that objects appear in a different place from where they actually are. Some might appear upside down in the sand, so that a patch of sky seems to be water, and in other places you can see objects that might actually be over the horizon. You can photograph mirages but, like the end of the rainbow, you’ll never find one.